Braking alternating-current motors.



E. F. W. ALBXANDERSON. BRAKING ALTERNATING CURRENT MOTOR.

APPLICATION FILED JUNE 4, 1906.

Patented A112. 16, 1910.

WVEA TOH: Ernst FW/l/exanderson fit 2f y.

WWW/36655 greater than its resistance, so that the ourat the source.

tromotive force.

. UNITED STATES PATENT OFFICE.

ERNST I. W. ALEXANDNRSON, OI! SCHENECTADY, NEW YORK, ASSIGNOB TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

Specification of Letters Patent. Patented Aug; 16 1910.

Application filed June 4, 1906. Serial No. 820,048.

To all whom it may concern:

Be it known that I, ERNST F. W. ALEX- axnnnson, a subject of the King of Sweden, residing at Schenectady, county of Schenectady, State of New Yor have invented certain new and useful Improvements in Braking Alternating-Current Motors, of which the following is a specification. Y

My invention relates to the control of alternating-current motors of the commutator type, and its object is to rovide an efiicient arrangement for braiing such motors.

The method of brakin direct-current motors by connecting the eld in shunt to the armature is well known in the art, but this simple connection will not suflice' for braking alternating-current motors, since the current in the motor field, being entirely inductive, will lag nearly ninety de ees be hind the impressed voltage, an consequently the induced armature volta e will be practically ninety de ees out 0 phase with the line-voltage. *ith such a phaserelation obviously no power can be returned to the line. If a voltage substantially 190 out of phase with the voltage at the source is impressed on the field it produces a current in the field substantially in phase with orin opposition to the voltage at the source, so that the induced armature voltage may practically be in opposition to the voltage In this manner ideal conditions for no load may be obtained,that is, with the induced armature voltage equal and opposite to the voltage of the source, so that no current flows; but when the armature voltage is raised-without shifting its phase in order to return energy to the line, the current that flows is so nearly wattless that very little energy is in fact returned. IThe reason for this is, that the reactance of the armature circuit of the motor is very much rent lags by a large angle behind the elecor instance, assume that theimpeda-nce of the armature circuit is entirely reactance; then if the armature voltage. is in opposition in phase to the line-- voltage, and is increased 111 amount sli htly above the line-voltage, the-resultant vo tage will be inphase' with the line voltage, but the current which will flow will be ninety degrees out of phase with the resultant of p Volta e, and consequently ninety degrees out ase with the line-Volta e. In other words, this current will be w olly wattless and will return no energy .to the line.

In order that the current may be nearly all energy-current, so that the braking is efficient, it is essential that the resultant voltage, produced by the line-voltage and induced armature-voltage as components, should be substantially ninety de rees out of phase with the line voltage. ith such degrees behind the resultant voltage, w

be in phase with the line-voltage, and con sequently will be an energy-current. Obviously, the induced armature voltage must be varied in order to vary the braking'efl'ect; but if the resultant voltage is to be maintairred at all times ninety degrees out of phase with the line-voltage, it is evident that the induced armature-Volta e must vary simultaneously in amount and 1n phase, so at all times the line-voltage, the induced armature-voltage, and the resultant volta e, will form a right-angle triangle, of which t e line-voltage is the base and is constant, while the induced armature-voltage is the hypotenuse and varies in amount and in position so as to vary the third side of the triangle, which is the resultant voltage and 'to which the braking efiect is proportional.

y invention, accordingly, consists in supplying to the field of the motor a current of proper phase and magnitude to induce in the armature a voltage which, with the voltage ofthe source, produces aresultant voltage substantially ninety degrees out of base with the voltage of the source, and urther consists in maintainin the phase of the resultant voltage substantially constant, while varying the phase and amount of the induced armature-voltage to vary the braking effect. Y

My invention will best be understood by reference to the accompanying drawings, in which Figure 1 shows diagrammatically an alter: netting-current motor of the commutator type arranged for braking in accordance with my invention; and Fig. 2 is a diagram of the phase relations of the electromotive .forces.

In the drawings A represents the armature, B the field winding, and C the compen- 65 a phase-relation, the current, lagging nineitfi' sating winding of a compensated series motor. I have selected this type of motor merely for the purpose of illustration, and it will be understood that my invention is equally applicable to any other commutator A controlling switch D is arranged to connect the type of alternating-current motor.

of these leads are connected across the source of voltage, while the third lead is connected through the secondary of a transformer G and through the primary of the transformer H to ground. The potential impressed upon the primary of transformer H, neglecting the efiect of the transformer G, would be substantially ninety degrees out of phase with the voltageof the source. Transformer G is inserted merely for the purpose of adjusting the phase of this voltage. This transformer, which supplies a component voltage in phase with the voltage of the source, may be employed to shift the phase of the voltage impressed upon the primary of transformer H, so as to reduce its displacement somewhat below ninety degrees from the phase of the voltage of the source. This phase adjustment is for the purpose of varying the braking efi'ect, as will be hereafter explained, and might equally wellbe obtained by shifting the terminal connections of tile phase-shifting transformer F, if des1re The secondary winding of transformer H is arranged to be connected to the field winding B when switch D is thrown into braking position. In this braking position the armature A and compensating winding C are connected directly across the line, while the field winding B is connected to the secondary of transformer H; the primary of which is placed in .a circuit in shunt to the motor armature, and thus furnishes a shunt excitation to the field. The field winding is thus connected in shunt to the armature through the phase-controlling transformers. A few turns 12. in series with the armature are placed on the core of transformer H. These turns furnish a. series excitation and are ar ranged to oppose the primary winding of the transformer. r

The operation of the apparatus shown in Fig. 1 will best be understood by reference -eeaeee toFig. 2. In this figure 00 represents the line-voltage, which is constant in phase and in amount. Of represents the hase of the voltage impressed upon the fiel windin B, due to the current in the voltageimpressed on the primary-of transformer H, is substantially ninety degrees out of phase with the line 0e, representing the voltage of the source: The field-current due to this voltage Of lags ninety degrees behind this voltage, and may be represented in phase by the line Ge which, consequently, represents the base of the shunt excitation. The induce armature-voltage due to this shunt excitation is in phase with it, and consequently may be represented in phase by the same line 06*. With a given adjustment of the transformer G the shunt excitation through fieldwinding B is constant, both in phase and amount, and consequently the induced armature-voltage due to the shunt exeitationwill lee-constant in -phase,but will vary in amount with the speed. The series turns it produce a series excitation, or in other words, a second component of the field-current, which is in phase with the armature-current. If, for a given speed of the armature, the induced voltage due to the shunt excitation is equal to O6, and the armature-current is re resented" in phase and inamount by t e line e 2' then this line may also represent the series excitation of the motor opposing the shunt excitation so that the resultant induced armature-voltage is represented by the line 06 The two component voltages 0e and 0?, representing respectively the voltage of the source and the induced armature voltage, give a resultant voltage e i, and this resultant voltage produces a current which, owing to the inductance of the motor circuit, lags substantially ninety degrees behind this voltage, and may be represented in amount and phase by the line ej This line is, of course, equal and parallel to the line 2' 6 It will be seen that this current is substantially in phase with the linevoltage 06 and is consequently an energycurrent. lfow, if the speed ofthe motor should change,for instance, increasing from the speed represented by O6 to the speed represented by Oe .it will be seen that the first effect would be to shift the position of the line e i, changing the phase of the current returned to the source; but this change of phase of the current and consequently of the series excitation increasesthe amount of the resultant voltage e 6 which also increases the amount of current returned to the line. This increased current conse uently increases the series excitation, whic is not only increased, but also shifted somewhat in phase. This inrimary win ing of transformer H. This vo tage,wh1ch IS in phase with, or rather in opposition to, the

66 by the effect of the series turns in the line ()2' tage, with the voltage of the source, produces e i,- which produces.

' produces a change comes creased series excitation maynbe indicated in phase-and amount by the e e 1?, giving an induced armature-voltage This induced armature-volthe resultant Volta thecurrent e 9'. bus, the increase in the series excitation due to the increase in speed tends to oppose the increase in amount of the induced armature-voltage, and instead in its phase; and by properly calculating the series turns the amount and base of the induced armature voltage may be caused to vary in such proportions that the will lie alon a line practically at rightangles to the line Oe, which means that the resultant voltage e i ez' etc., will increase in amount with varying speed, but will remain substantially constant in phase. Therefore, the current returned to the line will remain constant in phase, but will vary with the speed so as to give a stable and eflicient braking efi'ect.

The above discussion hasassumed that the phase of the volt-age impressed on the primary of transformer H has remained constant. Obviously, if it is desired to vary the braking eflect, to adapt the motor for difl'ereiit grades, for instance, in the'case of a railway motor, the phase of the shunt excitation should be varied, the amount being varied only sufiiciently to keep the rectangular relation between the resultant voltage and the line-voltage, it is evident that the adjustment of the transformerG will give precisely the desired variation. This transformer G may be manually controlled, thereby enabling the braking eflect to be varied at will, and for each adjustment of the transformer G the series turns it will automatically maintain the proper phase relation of the resultant volt-age for different speeds of the motor. Consequently, such an arrangement as described will give efiicient braking under all conditions.

It may be noted that if the voltage im pressed on .the primary of transformer H were maintained absolutely constant, the series turns it. could not afiect the amount or phase of the field current taken from the secondary of the transformer; but the primary of transformer His excited through the phase converter F, which is made as small as possible, and with high reactance and consequently poor regulation; so that the voltage supplied thereby has enough flexibility to be varied the desired amount the transormer H.

I have illustrated and described my invention as applied to a single motor. Obviously, it may be applied to any number of motors, and any desired means for producing the proper phase-displacement of the represented by points 11 1?, and 1', etc,

" shunt excitation may be em- --ployed, and with any desired arrangement of controlling switches. 1 While I have described my invention with particular reference tocontrolling the phase of the field excitation of an alternatingcurrent motor connected in shunt for braking purposes, it isobvious that my invention in certain of its aspects is equally a plicable to maintaining the proper phase re ation of,

field magnetization to armature current in any shunt connected alternating current. motor of the commutator type, whether this connection is employed simply for braking or for ordinary operation. In either case the series excitation which I have described and illustrated produces a stable condition of proper phase -relation under varying loads.

When I speak, in the appended claims, of connecti g the armature to the source, I do not mean that the armature is necessarily connected directly to the source, or that it is the only one of the motor windings connected to thesource; but I intend simply to state the essential fact that the armature in which the energy is generated is connected to the source to which the. energy. is to be returned, in any suitable manner for enabling the transfer of ener to be made. What I claim as new, and esire to secure by Letters Patent of the United States, is,- 1. The method of braking an alternatingcurrent motor of the commutator type which tage impressed on the field substantially ninety degrees from the voltage of the source, and controlling the phase of the field to vary the voltage impressed on the braking effect. 1 I

3. The method of braking an alternatingourrent motorof the commutator type which consists in connecting the armature to the source and supplying to the field a current of the proper phase and magnitude to induce 1n the armature a voltage, which, with vice adapted to shift the phase of the vol-' the voltage of the source, produces a result- .Vant voltage substantially ninety degrees out of phase with the voltage of the source.

4. The method of braking an alternating current motor of the commutator type which consists in connecting the armature to the source and supplying to the field a current of proper phase and magnitude to induce in the armature a voltage, which, with the voltage of the source, produces a resultant voltage substantially ninety degrees out of phase with the voltage of the source and maintaining the phase of said resultant voltage substantially constant for varying braking loads.

5. The method of braking an alternatingcurrent motor of the commutator type which consists in connecting the armature to the source and supplying to the field a current of the proper phase and magnitude to-induce' in the armature a voltage, which, with the voltage of the source, produces a resultant voltage substantially ninety degrees out of phase with the voltage of the source and maintaining the phase of said resultant-voltage substantially constant while varying the phase and amount of the induced armature voltage to vary the braking efiiect.

6. In combination, an alternating-current motor of the commutator type, a source of current therefor, and means for connecting the motor armature to the source, means for impressing on the motor field a voltage substantially ninety degrees out of phase with the voltage of the source to brake the motor, and means for controlling the voltage impressed on the field. V

7. In combination, an alternating-current motor of the commutator type, a source of current therefor, and means for connecting the motor armature to the source, means for impressing on the motor field a voltage substantially ninety degrees out of phase with the voltage of the source to brake the motor, and means for controlling the amount and phase of the voltage impressed on the field.

8. In combination, an alternating-current motor of the commutator type, a source or" current therefor, and means for connecting the motor armature to the source, means for impressing on the motor field a voltage substantially'ninety degrees out of phase with the voltage of the source to brake the motor, and means for controlling automatically the amount and phase of the voltage impressed on the field with variation in armature current.

9. In combination, "an alternating-current motor ofthe commutator type, a source of current therefor, and means for connecting the armature to the source, means for impressing on the field a voltage of proper magnitude and phase for producing a fiow of current from armature to said source substantially in opposition in phase to the voltage ofthe source.

10. In combination, an alternating-current motor of the commutator type, a source of current, means for connecting the motor armature to the source, a phase shifting device, means for connecting the motor field in shunt to the armature through said device, and means for automatically controlling the e emea phase of the field magnetization with varia= tion in armature current.

11. In combination, an alternating-current motor of the commutator type, a source of current therefor, and means for connecting the motor armature to the source, means for impressing on the motor field a voltage sub stantially ninety degrees out of phase with the voltage of the source, and means for controlling automatically the phase of the field magnetization with variation in armature current.

12. In combination, an alternating-current motor of the commutator type, a source of current therefor, and means for connecting the armature to the source, means for impressing on the field a voltage of proper magnitude and phase for producing at the armature terminals a voltage which with the voltage of the source produces a resultant voltage substantially ninety degrees out of phase with the Voltage of the source.

13. In combination, an alternating-current motor of the commutator type, a source of current therefor, means for connecting the motor armature to the source, a phase-shifting device, means for connecting the motor field in shunt to the armature through said device, and a winding in series with the armature adapted to vary the amount and phase of the field magnetization.

14. In combination, an alternating-current motor of the commutator type, a source of current therefor, a phaseshifting transformer, means for connecting the motor armature to the source, means for connecting the motor field to the source through the phase-shifting transformer, and a trans former winding in series with the armature adapted to vary the amount and phase of l the voltage impressed on the field.

15. In combination, an alternating-current motor of the commutator type, a source of currenttherefor, means for connecting the motor armature to the source, means for impressing on the field a voltage substantially ninety degrees out of phase with the voltage of the source for braking, and a winding in series with the armature adapted to vary the amount and phase of the field magnetization.

16. In combination, an alternating-current motor of the commutator type, a sourceol current therefor, means for connecting the motor armature to the source, means for impressing on the field voltage substantially ninety degrees out of phase with the voltage of the source for braking, a winding in series with the armature adapted to vary the amount and phase of the field magnetization, and manuall -controlled means for controlling the field magnetization to vary the braking effect.

17. In combination, an alternating-current motor of the commutator type, a source of lOO ' voltage impressed on the field.

8 In combination, an alternating-current motor of the commutator type, a source of single-phase current, -means for deriving rom 'said source and impressing on said fielda voltage displaced substantially ninety degrees from the voltage of said source, and means for automatically controlling the phase of the field magnetization with variation of the armature current.

-19. In combination, an alternating-current motor of the commutator type, a source of single-phase current, means for deriving from said source and impressin on said field for braking a voltage disp aced substantially ninety degrees from the voltage of said source, meansfor automatically con.- trollin the field magnetization with variation 0 the armature current, and manuallycontrolled means for controlling thefield megnetization.

20. In combination, an alternating-currentmotor of the commutator type, a source of current therefor, means for connecting the motor armature to the source, means for impressing on the field a component voltage displaced in phase substantially ninety degrees from the voltage of the source, and means for impressing on the field a variable component voltage 'a proximately in phase with the voltage of t e source.

21. In combination, an alternating-current motor of the commutator type, a source of single-phase current, means for connecting the motor armature to the source, and means for deriving from the source and impressing on the motor field two component voltages, one displaced in phase substantially ninety degrees from the voltage of the source and the other variable in amount and approximately in phase with the voltage of the source.

'22. In combination, an alternating-current motor of the commutator type, a source of current therefor, means for connecting the motor armature to the source, means for impressing on' the field a component voltage displaced in phase substantially ninety de grees from the voltage of the source, means or impressing on the field a variable component voltage approximately in phase with the voltage ofthe source, and a winding in series with the armature adapted to vary the field excitation.

' 23. In combination, an alternating-current motor of the commutator type, a source of single-phase current, means "for connecting the motor armature to the source, means for deriving from the source and impressing on the motor field two component voltages, one

"displaced in grees, from t the other variable in amount and approxi- -source, and a that supplies cuit and en phase substantially ninety dee voltage of the source and mately in phase with the voltage of the winding in series with the armature adapted to vary the field excitation.

24.- The combination with an alternating current distributing circuit, and a generator current thereto, of means for deriving current from the distributing cirplying the same to the field magnet'win ing of the generator, and means for adjusting the phase of the current supplied to the distributing circuit with respect :to the electromotive force of said circuit.

25.;The combination with an alternating current distributing circuit, and a generator that supplies current thereto, of an exciter that supplies thefield magnet winding of the generator having its field magnet Winding connected to the distributing circuit, and means for adjusting the phase of the generated electromotive force with respect to the electromotive force of the distributing circuit so as to cause the current supplied to the distributing circuit to agree approximately in phase with the electromotive force of the circuit.

26. The combination with an alternating current'distributing circuit, and a generator that supplies current thereto, of an exciter that supplies the field magnet winding of the generator-having its field magnet winding connected to thedistributing circuit, and means for adjusting the phase of the generated electromotive force with respect to the electromotive force of the distributing circuit.

27. The combination with an alternating current distributing circuit, and a generator that supplies current thereto, of means for adjusting the phase of the current in the field ma et winding of the generator to eifect ad ustment of the phase relations of the current supplied to the distributing circuit and the electromotive force thereof.

28. The combination with an alternating current distributing circuit, and a generator that supplies current thereto, an eXciter that supplies the field magnet winding of the generator and has its field magnet winding connected to the distributing circuit, and means in circuit with the field magnet winding of the generator for adjusting the phase of the current supplied to the distributing circuit with respect to the electromotive force of the circuit.

29. The combination with an alternating current distributing circuit, a dynamo-electric machine having its armature connected thereto, and a dynamo-electric machine that supplies alternating exciting current to the aforesaid machine, of means for applying an auxiliary alternating electromotive force senses to the field magnet Winding of the dynamoeiectric machine an auxiliary electroinotive force that is out of phase with the electromotive force of the exciter.

In Witness whereof, I have hereunto set my hand this 2nd day of June, 1906.

ERNST F. W. ALEXANDERSON.

Witnesses:

HELEN ORFORD, Gr. (3. Honms'rnn. 

